FIG. 1 shows a ducted fan gas turbine engine 10 comprising, in axial flow series: an air intake 12, a propulsive fan 14 having a plurality of fan blades 16, an intermediate pressure compressor 18, a high-pressure compressor 20, a combustor 22, a high-pressure turbine 24, an intermediate pressure turbine 26, a low-pressure turbine 28 and a core exhaust nozzle 30. A nacelle 32 generally surrounds the engine 10 and defines the intake 12, a bypass duct 34 and a bypass exhaust nozzle 36.
Air entering the intake 12 is accelerated by the fan 14 to produce a bypass flow and a core flow. The bypass flow travels down the bypass duct 34 and exits the bypass exhaust nozzle 36 to provide the majority of the propulsive thrust produced by the engine 10. The core flow enters in axial flow series the intermediate pressure compressor 18, high pressure compressor 20 and the combustor 22, where fuel is added to the compressed air and the mixture burnt. The hot combustion products expand through and drive the high, intermediate and low-pressure turbines 24, 26, 28 before being exhausted through the nozzle 30 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines 24, 26, 28 respectively drive the high and intermediate pressure compressors 20, 18 and the fan 14 by interconnecting shafts 38, 40, 42.
The main gas path within the high, intermediate and low pressure turbines is bounded by a series of axially adjacent components. These will typically be seal segments which sit radially outboard of the rotating blades, and so-called platforms which are located radially outboard and often integral with nozzle guide vanes. These axially adjacent components experience axial and radial loads and relative movement in use and also need to be sealed across to prevent excessive leakage of air into the main gas path.
U.S. Pat. No. 5,188,507 shows a turbine shroud formed by a ring of butted shroud segments. Each turbine shroud segment has a radially inwardly projecting annular flange which is seated on a radially outwardly facing surface of an annular tip of the outer shroud of the downstream nozzle stage. This flange is free to slide axially relative to the annular tip during thermal expansion of the nozzle outer shroud in the axial direction. Each turbine shroud segment has a spring seated thereon which urges the radially inwardly projecting flange toward the annular tip of the nozzle outer shroud.
WO2014/168804 a blade outer air seal (BOAS) for a gas turbine engine. The BOAS includes a seal body having a radially inner face and a radially outer face that axially extend between a leading edge portion and a trailing edge portion. A retention flange extends from one of the leading edge portion and the trailing edge portion and a seal contacts the retention flange.
The present invention seeks to address one or more of these issues.